Silicon photodiodes are used as photo detectors, that is as optical data acquisition devices, in optical data transmission systems. Photodiodes are also used as power sources for small portable electronic devices, such as hand held calculators, as well as higher voltage power sources for satellites and other devices which do not have other sources of power available.
In general, these two uses of photodiodes are normally thought of as being mutually exclusive. The photodiodes used for data acquisition tend to be very small, low capacitance devices which can handle high data transmission rates. The photodiodes used for power generation tend to be large, high capacitance devices because a large diode junction is required to produce a significant amount of power. However, the high capacitance of the power generating photodiodes precludes a high rate of data acquisition. For instance, the photodiode array used to power a small calculator has been found by the inventor to have a typical maximum bandwidth of 300 hertz, which is many orders of magnitude less than the data rates found in typical optical data transmission systems.
The present invention is useful in applications in which relatively low data rates, such as 60 or 120 bits per second, is useful. In particular, the present invention is directed to low power devices which use a photodiode array to eliminate the need for a battery and the need for a keyboard or equivalent input device. Such applications include programmable displays and certain types of security locks.